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Serum or plasma concentration of vitamin B12 (cobalamin)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of vitamin B12 in your blood. Vitamin B12 is essential for red blood cell production, nerve function, and DNA synthesis.

Quick summary

["Vitamin B12 helps prevent anemia and supports nerve health."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
5201-9
Short code
HDV Ab Ser RIA-aCnc
Synonyms
HDV Ab Ser RIA-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ria
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why Might You Need This Test?

Your doctor may order this test if you have symptoms like fatigue, weakness, numbness, or tingling in your hands and feet. It may also be checked during routine blood work, especially if you have conditions like pernicious anemia, celiac disease, or other nutritional deficiencies.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it involves drawing blood from a vein. If you’re taking vitamin B12 supplements, your doctor may advise stopping them temporarily.

How the Test Is Performed

A healthcare provider will collect a blood sample from a vein in your arm using a needle. The sample is then sent to a lab for analysis.

What the Results Mean

Low levels of vitamin B12 can indicate deficiencies, which may require dietary changes, supplements, or medical treatment. High levels may be due to overconsumption or certain medical conditions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Vitamin B12 deficiency can lead to serious health issues, including anemia, nerve damage, and cognitive problems. Early detection and treatment can help prevent complications.

Short name

Vitamin B12 Level

Frequently asked questions

Could vitamin B12 levels be affected by certain medications?
Yes, some medications—like proton pump inhibitors (used for acid reflux), certain antibiotics, or antacids—can interfere with vitamin B12 absorption. Always discuss your medications with your doctor.
Is there a difference between serum and plasma vitamin B12 testing?
Both tests measure the same analyte, but plasma is blood without clotting factors, while serum is blood after clotting. The lab method will specify which type was used.
How often should I get this test?
Your doctor will determine the frequency based on your health status, symptoms, or risk factors. Regular monitoring may be recommended if you have conditions like pernicious anemia or chronic kidney disease.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy